PCF8533 datasheet(18/36 Pages) PHILIPS

18 / 36 page

1999 Jul 30

Philips Semiconductors

Product speciﬁcation

Universal LCD driver for low multiplex rates

PCF8533

CHARACTERISTICS OF THE I2C-BUS

The I2C-bus is for bidirectional, two-line communication

between different ICs or modules. The two lines are a

Serial Data line (SDA) and a Serial Clock Line (SCL). Both

lines must be connected to a positive supply via a pull-up

resistor when connected to the output stages of a device.

Data transfer may be initiated only when the bus is not

busy.

By connecting SDAACK to SDA on the PCF8533, the SDA

line becomes fully I2C-bus compatible. Having the

acknowledge output separated from the serial data line is

advantageous in Chip-On-Glass (COG) applications.

In COG applications where the track resistance from the

SDAACK pad to the system SDA line can be significant, a

potential divider is generated by the bus pull-up resistor

and the Indium Tin Oxide (ITO) track resistance. It is

possible that during the acknowledge cycle the PCF8533

will not be able to create a valid logic 0 level. By splitting

the SDA input from the output the device could be used in

a mode that ignores the acknowledge bit. In COG

applications where the acknowledge cycle is required, it is

necessary to minimize the track resistance from the

SDAACK pad to the system SDA line to guarantee a valid

low level.

The following definition assumes SDA and SDAACK are

connected and refers to the pair as SDA.

7.1

Bit transfer

One data bit is transferred during each clock pulse.

The data on the SDA line must remain stable during the

HIGH period of the clock pulse as changes in the data line

at this time will be interpreted as a control signal. Bit

transfer is illustrated in Fig.10.

7.2

START and STOP conditions

Both data and clock lines remain HIGH when the bus is not

busy. A HIGH-to-LOW transition of the data line, while the

clock is HIGH is defined as the START condition (S).

A LOW-to-HIGH transition of the data line while the clock

is HIGH is defined as the STOP condition (P). The START

and STOP conditions are illustrated in Fig.11.

7.3

System conﬁguration

A device generating a message is a ‘transmitter’, a device

receiving a message is the ‘receiver’. The device that

controls the message is the ‘master’ and the devices which

are controlled by the master are the ‘slaves’. The system

configuration is illustrated in Fig.12.

7.4

Acknowledge

The number of data bytes transferred between the START

and STOP conditions from transmitter to receiver is

unlimited. Each byte of eight bits is followed by an

acknowledge bit. The acknowledge bit is a HIGH level

signal put on the bus by the transmitter during which time

the master generates an extra acknowledge related clock

pulse. A slave receiver which is addressed must generate

an acknowledge after the reception of each byte. Also a

master receiver must generate an acknowledge after the

reception of each byte that has been clocked out of the

slave transmitter. The device that acknowledges must

pull-down the SDA line during the acknowledge clock

pulse, so that the SDA line is stable LOW during the HIGH

period of the acknowledge related clock pulse (set-up and

hold times must be taken into consideration). A master

receiver must signal an end of data to the transmitter by

not generating an acknowledge on the last byte that has

been clocked out of the slave. In this event the transmitter

must leave the data line HIGH to enable the master to

generate a STOP condition. Acknowledgement on the

I2C-bus is illustrated in Fig.13.

7.5

PCF8533 I2C-bus controller

The PCF8533 acts as an I2C-bus slave receiver. It does

not initiate I2C-bus transfers or transmit data to an I2C-bus

master receiver. The only data output from the PCF8533

are the acknowledge signals of the selected devices.

Device selection depends on the I2C-bus slave address,

on the transferred command data and on the hardware

subaddress.

In single device application, the hardware subaddress

inputs A0, A1 and A2 are normally tied to VSS which

defines the hardware subaddress 0. In multiple device

applications A0, A1 and A2 are tied to VSS or VDD in

accordance with a binary coding scheme such that no two

devices with a common I2C-bus slave address have the

same hardware subaddress.

7.6

Input ﬁlters

To enhance noise immunity in electrically adverse

environments, RC low-pass filters are provided on the

SDA and SCL lines.

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